I have a Miroku / Browning ML/BL22. It is a used rifle which hasn't been treated very well by the former owner so there is some rust. I have used 000 and some wd40 to clean the rust pitting. I rube for a few minutes and as soon as the steel wool is crushed and compacted I wipe down the rifle and take a new piece of steel wool.
Now to my problem, the srew in the barrelband is really tight. I can't get it to losen. I don't wan't to be overly aggressive so I have now bought some freeze spray (-40°C/-40°F). Does anybody have any experience with this method? I don't think that using a propane torch is an option for this really small screw and fear that the damage to the aluminium is imminent.

Propane torch to warm up the screw would be OK just keep it within about 150 C. I've never tried freezing.But whether heating or freezing the process depends on different coefficient of thermal expansion to loosen things.

Try automatic transmission fluid and acetone mix 50/50 and soak it for a few days.

This is the real deal. I recently started using this at work after reading about it in other threads here. Hands down it blows away anything store bought. Just keep it shook up well, as it stratifies very quickly.

I am reluctant to try a propane torch on the aluminium part. I believe it to be either anodized or painted. I'm not sure that it will tolerate heat very well. The screw is very small so the heat is impossible to concentrate only on it.

These are all just WAG's on my part. I would try kroil or PB Blaster first. then I would try a soldering iron on the head of the screw. Be sure to clean off all the Kroil before using heat. Make sure the driver fits perfect before you turn the screw. Also, you might be able to break it free by attempting to tighten it a bit if it will not come out. One more thing might be to peck on the end of the driver with a hammer to vibrate it a bit.

Unfortunately,it just sometimes happens that a steel screw inserted dry into aluminum threads seems to bond together.Try all the lube,maybe will work.
Warming some might help,but I'd be wary.If its aluminum,the cosmetic finish is as likely to be paint as black anodize.
A problem with your cold spray,the coefficient of expansion of aluminum is greater than that of steel.So,when you freeze it,the aluminum female thread will shrink faster than the steel screw.Thats tighter!

It may help to cycle it through cold,but don't try unscrewing it cold.

Consider this:Odds are good the screw will break off.If that happens,unless you have a mill and know how,you will likely completely mangle it trying to drill it out.

If there is a smith or shop who has a mill,let them do it before you break the screw.Let them break the screw,if it is going to break.

It is one of the greatest penetrants I have ever used. You get it at your local health food store (NOT Walgreen's et. al.) for about $3.00-4.00 for a small bottle. You don't need a lot of it, however, as it seeps right into any crevice, and generally a few drops are all you need.

Give it a try. I have gotten more old, rusty, corroded screws out using it, as well as barrels from old Italian Vetterli rifles.

Thank you all for your help and good recomendations. Many of the products you have discribed are not available here in Austria so I am thinking about letting my gunsmith have a try. ATV fluid is my second option.

Try the ATF (Dexron)/acetone soak. It really works. When you replace the bolt put a little anti seize compound on the threads. Any time you run a steel fastener into alum. threads anti seize compound will save you down the road. Ask any biker or aircraft mechanic. Anti seize compound should be available at any auto parts store.

In the old days movie houses used carbon torches, I have a carbon torch that attaches to my electric welder, and when needing to heat a small area for what ever, I sharpened a carbon stick, insulated one end and attached an electric lead, then attached another lead to the work to be heated, then attached the leads to a 12 volt auto battery, no one believes how effective something that simple works.

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